The domestication of the wolf larynx – testing the neural crest connection

The Neural Crest Domestication Syndrome (NCDS) hypothesis suggests that
selection pressures for tameness during animal domestication result in a
down-regulation of neural crest cell migration and proliferation,
providing a mechanistic explanation to traits commonly observed across
domesticates. We test the viability of this hypothesis via a derived
prediction. According to the NCDS hypothesis, neural crest-derived
structures should be reduced throughout the entire organism in
domesticated variants compared to their wild ancestors. Here we test this
prediction by comparing the larynx of the wolf and the domestic dog.
Anatomical landmarking of the cricoid and thyroid cartilages confirmed
absolutely and relatively shorter vocal folds and smaller larynges in
mesocephalic dogs compared to wolves. Additional quantification of the
laryngeal anatomy shows normal (mesocephalic) dogs to have a smaller
cricoid diameter and shape-altered thyroid shields. As an exploratory
extension, we further quantify the concrete anatomical changes to the
laryngeal cartilages caused by brachycephaly, finding that a flattened
thyroid shield and ventral cricoid ring fit the symptomatic descriptions
of laryngeal collapse. Our comparison of larynges of wolves and dogs are
in line with the NCDS-derived prediction and support the validity of the
Neural Crest Domestication Syndrome Hypothesis.